In connecting together a series of individual casing segments or other tubulars and running the assembled string down a well, each tubular is typically first lifted up into the well derrick structure. The lower end of each suspended tubular is then added to the tubular string by threadedly connecting the lower end of the suspended tubular to the upper end of the string at a point of connection near the rig floor. During the connecting operation, the upper end of the assembled string is typically held by a rotary table, spider or other gripping device located on the rig floor such that the remainder of the string is suspended in the well. When the connection is completed, the gripping device at the rig floor is released in order to allow the newly attached section to be lowered into the well. Once lowered, the upper end of the added section is then gripped at the rig floor by the rotary gripping device so that the next tubular section can then be lifted into the derrick and threadedly connected to the assembled string.
A prior art derrick system for assembling a string of casing segments or other tubulars and running the assembled tubular string down a well is described in U.S. Pat. No. 4,921,386. The entire disclosure of U.S. Pat. No. 4,921,386 (hereinafter referred to as the '386 patent) is incorporated herein by reference. The prior art derrick system 2 described in the '386 patent is schematically illustrated in FIG. 1. The prior art system 2 comprises: a rig floor or drilling platform 4; a rotary table system or other gripping device 6 which holds the upper end 8 of the assembled string; a derrick structure 10; a suspended traveling block and swivel assembly 12 which can be operated for lifting, suspending, and lowering additional tubular segments 14 within derrick 10; and a stabbing apparatus 20 positioned within derrick 10 for stabbing the suspended tubular section 14. As used herein, the term “stabbing” refers to the operation of stabilizing, positioning, aligning, and/or otherwise directing the lower end of the suspended tubular segment 14 into engagement with the upper end of the tubular string 8 for connecting the lower end of the tubular segment 14 to the upper end of the tubular string 8.
The prior art stabbing apparatus 20 described in the '386 patent is depicted in FIGS. 2 through 5. The prior art stabbing apparatus 20 includes: a bracket and base assembly 22 which can be removably secured to or on a derrick cross-member or other structure within derrick 10; a boom assembly 24 which is pivotably secured to the bracket and base assembly 22 for up and down movement; and a remote control system 26 which is used for operating the stabbing apparatus 20. It has also been known heretofore that a single stabbing apparatus of this type can be mounted on a track for vertical movement within the derrick.
The boom assembly 24 of prior art stabbing apparatus 20 comprises: a telescoping boom 28 which can be extended and retracted; a pair of grasping members 30 carried on the distal end of boom 28; an internal piston and cylinder assembly 32 for extending and retracting the boom 28; a lifting piston and cylinder assembly 34 connected between the boom assembly 24 and the bracket and base assembly 22 for pivoting the boom assembly 24 up and down; a limit switch assembly 35 which will detect that the boom assembly 24 has reached a desired horizontal position and will then prevent the boom assembly from pivoting further downward; a yawing piston and cylinder assembly 36 for pivoting the boom 28 from side-to-side; and a boom housing structure 38 which holds the boom 28 and the yawing piston and cylinder assembly 36 in a manner effective for enabling the yawing piston and cylinder assembly 36 to be operated without interfering with the lifting piston and cylinder assembly 34.
The boom housing structure 38 includes a box structure 40 in which the base of the boom 28 and the base of yawing piston and cylinder assembly 36 are each pivotably retained for side-to-side movement. The boom housing structure 40 also includes a bottom plate structure 42 which extends forwardly from the bottom of the box 40. The distal end of the lifting piston and cylinder assembly 34 is attached to the plate structure 42 for lifting both the boom 28 and the boom housing structure 38.
The lifting piston and cylinder assembly 34 of the prior art stabbing apparatus 20 is operable for pivoting the boom assembly 24 between a substantially horizontal operating position, as illustrated in FIG. 1, and a substantially vertical clearance position. As used herein, “substantially horizontal” refers to a position which is within +/−5° of true horizontal.
The grasping members 30 of the prior art stabbing apparatus 20 are a pair of jaw structures which are retained on the distal end of boom 28 by a jaw bracket 44. The proximal ends of the jaws 30 are pivotably retained in the jaw bracket 44 by pivot pins 46. A lateral piston and cylinder assembly 48 is connected between the proximal ends of jaws 30 for pivoting the jaws 30 between an open position for receiving and releasing the suspended tubular segment 14 and a closed position (shown in FIG. 2) for grasping the suspended tubular 14. Radially adjustable rollers 50 are provided in the jaws 30 for contacting and holding the suspended tubular 14 while also allowing the tubular 14 to be rotated within the jaws 30 for threadedly connecting the tubular 14 to the upper end of the tubular string 8.
The remote control system 26 of the prior art stabbing apparatus 20 includes a bank assembly 52 of valves. The valve bank 52 is removably secured above the boom housing box 40. The valves are electrically operated solenoid-type valves, each of which is used to control hydraulic fluid flow to a separate one of the piston and cylinder assemblies 32, 34, 36, and 48 used for extending the boom 28, pivoting the boom 28 from side-to-side, pivoting the boom assembly 24 up and down, and opening and closing the grasping members 30.
The remote control assembly 26 also includes: a hand-held remote 54; a bundle of electrical leads 56 extending from the hand-held remote 54 to the valve bank 52 for operating and controlling the various solenoid valves; four switches 56-62 provided on the hand-held remote 54 for separately operating the extending, lifting, yawing, and grasping piston and cylinder assemblies 32, 34, 36, and 48; and a guard 64 provided on the hand-held remote over the toggle switches 56-62 for protecting the toggle switches from damage and for preventing the switches from being inadvertently actuated in the event that the hand-held remote is dropped.